Blood coagulation factor IX is absent or deficient in hemophilia B patients. Current therapy, the transfusion of human whole blood components, is effective, but it is not prophylactic or free of risk. The long term objective of this research proposal is the development of a somatic cell gene therapy for hemophilia B. Autologous capillary endothelial cells from adipose tissue of a hemophilia B patient will be isolated, transduced with the factor IX gene using a replication- incompetent retrovirus, and grown in a 3-dimensional (3-D) collagen matrix for implantation into the same patient. Capillary endothelial cells in 3-D matrices form tube-like structures that are anticipated to anastomose with the patient's vasculature and become perfused with blood when implanted in the patient. In this way, factor IX will be chronically secreted directly into the patient's blood, alleviating the clinical manifestations of hemophilia B. In Phase I of this SBIR grant application animal models will be used to determine the feasibility of this therapeutic approach. Rat and mouse capillary endothelial cells (RCEC and MCEC) will be isolated and transduced with retroviruses that encode human growth hormone (hGH), human apolipoprotein E (ApoE) and human factor IX. RCECs, transduced with hGH and packaged into 3-D matrices, will be implanted to determine whether anastomosis occurs and whether hGH will be secreted and detectable in the plasma. MCECs, transduced with ApoE, and packaged into 3-D matrices, will be implanted in ApoE-deficient mice. Secreted recombinant ApoE from implanted MCECs is expected to cause a decrease in the high serum cholesterol in these mice and delay atherogenesis, indicating that therapeutic benefit can result from this approach. Finally, capillary endothelial cells will be isolated from human adipose tissue, transduced with factor IX, and packaged into 3-D matrices. Factor IX production by these cells, together with the animal studies, will demonstrate the feasibility of this therapy in humans.